Coil with adjustable permeability



Dec. 3, 1968 R. H BARDEN COIL WITH ADJUSTABLE PERMEABILITY Filed May 9, 1966 l N VENTOR. RICHARD H. BARDE/V A TTORNEYS.

H95 HIP O h 9 United States Patent 3,414,857 COIL WITH ADJUSTABLE PERMEABILITY Richard H. Barden, 440 N. Adams, Sierra Madre, Calif. 91024 Filed May 9, 1966, Ser. No. 548,578 2 Claims. (Cl. 336-233) ABSTRACT OF THE DISCLOSURE This invention relates to a means for adjusting the permeability of ring-shaped cores. An annular ring for a toroidal coil has an arcuately extending internal void that extends for a substantial portion of the arcuate length of the ring. Access is provided to this void, and a quantity of magnetizable material, discretely divided and dispersed in a settable medium, is injected into the void, without filling it, whereby further adjustment of the permeability can be made by injection of additional such material and medium.

This invention relates to toroidal coils and in particular to means for adjusting the permeability of their ringshaped cores.

When toroidal coils are manufactured, it is customary to take a ring made of magnetizable material, such as iron or processed ferrites, and wind the desired number of turns upon the ring. The properties of the coil are in large part derived from the magnetic properties of the core, particularly of its effective permeability. These torodial coils are used in a wide variety of installations in which close control over their properties is desirable, especially as it relates to its environment and to associated circuitry. It is not uncommon for a circuit made up of elements which are properly designed for the circuit to be tuned, not to be tuned because of minor tolerance errors in the core or in some component of the associated coil, or even because of environmental elements such as a metal case. It is desirable to have means for adjusting the effective permeability of the ring-shaped core in order to control the properties of the coil and bring it (and the circuitry) up to the desired conditions. Means for this purpose have hitherto been attempted but have not been known to be successful for a number of reasons. One is that these rings are often very small and a fairly large percentage change of effective permeability is desirable.

No means has heretofore existed which enabled an already-constructed coil to be brought to some optimum condition without changing the number of turns, or of altering the gross shape or construction of the ring itself. Obviously it is a desirable objective to be able to adjust an already-manufactured core by controlling the effective permeability with simple means rather than, for example, changing the number of turns (which might be off count) or to attempt other means for correcting accumulated tolerance errors as to effective permeability such as by disassembling the coil and grinding down the ring. It is an object of this invention to provide a method and apparatus for accomplishing such an adjustment.

This invention includes an annular ring for a toroidal coil, which ring has an axis and a concentric inner and outer wall, these walls being joined by a pair of axially spaced-apart boundary walls. The ring has an internal void that extends arcuately within the walls for a substantial portion of the arcuate length of the ring. Access means passes through one of said walls into the void through which a magnetic material can be inserted to adjust the permeability of the ring.

According to a preferred but optional feature of this invention, a magnetizable material is provided which is discretely divided and dispersed in a settable medium which is injectible into said void.

Patented Dec. 3, 1968 According to another preferred but optional feature of the invention, the material is in flexible elongated form so as to be insertable through the access means.

Accordingitostill another preferred but optional feature of the invention, the material may be formed as a strip into a loop, part of which loop is a non-magnetic material which can be adjustably positioned in the void so as to vary the proportion of magnetic to non-magnetic material in the void.

The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings, in which:

FIG. 1 is a side elevation of the presently preferred embodiment of the invention;

FIG. 2 is a fragmentary cross-section taken at line 2--2 of FIG. 1;

FIG. 3 is a top view of FIG. 2;

FIG. 4 is a cross-section of still another embodiment of the invention;

FIG. 5 is a cross-section schematically illustrating one of the methods of the present invention;

FIG. 6 is a sectional illustration of the presently preferred embodiment of the invention;

FIG. 7 is a sectional drawing of still another embodiment of the invention; and

FIG. 8 is an elevation of a portion of FIG. 7.

FIG. 1 shows a toroidal coil comprising coil 10 comprising a plurality of turns 11 of Wire wound upon a ring 12. This ring and the other rings described herein are made of magnetizable material in accordance with well-known inductive principles. An advantage of the instant invention is that it is adaptable to use with powdered metallurgy technique, and the rings may readily be formed by compressing iron powder, such as carbonyl iron powder Grade E as manufactured and sold by General Aniline & Film Corporation, 435 Hudson St., New York 14, N.Y., with about a 5% phenolic binder into a solid cohesive structure. This iron powder is precipitated from iron carbonyl and has a particle size approximating eight microns, which is suitable for powder metallurgy. It is to be recognized that other magnetic materials are suitable, including ferrites which are before processing non-magnetic, and also that the ring may be formed from a solid piece, instead of from compressed particulate material.

FIGS. 2 and 3 illustrate one-half of ring 12, it being recognized that mirror images will be furnished: The ring has a central axis 13, an inner wall 14, an outer wall 15 and a pair of boundary walls 16 and 17, joining the inner and outer walls. In the embodiment shown, the cross-section is circular, and the walls as defined are the inner, outer and edge portions thereof.

An internal void 18 is formed as a groove in one or both of the mirror image parts and extends for a substantial portion of the periphery of the ring, the term substantial in this case meaning 30% or more of the arcuate length thereof.

Parts 19, 20 are shown joined to form an integral ring in FIG. 1. FIG. 3 shows access means 21in this case a port, for access to the central void. When the halves are joined to form ring 12, access means 21 forms a circular port which is subject to use as shown in FIG. 5.

In FIG. 5 the effective permeability of the ring is shown being adjusted by the injection of magnetic material 22 comprising in the illustrated example a slurry of magnetic material such as iron powder or fillings suspended in a settable composition, such as an epoxy resin or varnish. This slurry, while still in the fluid state, is placed in a syringe 23 that 'has a nozzle 24 which makes a close fit with access means 21. This material is injected into the void from the syringe until an amount of magnetic material suitable to adjust the gross (or effective) permeability of the ring is supplied. If desired, an approximation can 3 be made of an appropriate proportion of magnetic material in the fluid so that the entire void can be filled, leaving no void, but instead just the right amount of solid to fill the void and adjust the effective permeability to a desired level.

FIG. 4 illustrates still another embodiment of the invention showing a half ring 25. This half ring and a mating mirror image part (not shown) will, when assembled together, form inner, outer and boundary walls as in FIG. 1 and will also include a void 26 together with access means 27. This embodiment illustrates a different means of adjusting the permeability of the ring which comprises a coil 28 of magnetic material such as iron Wire or strip which may be adjustably pushed into or pulled out of the void, and cut off at the surface when the desired amount is in the void. Preferably, but not necessarily, the coil will include at least one full convolution.

FIG. 6 shows another half ring 29 which, with its mirror image, will be formed into a ring as in FIG. 1, the void 30 having access means comprising a pair of ports 31 and 32 connected by a groove. Wire or strip may be inserted or pulled out as in FIG. 4 or material may be injected as in FIG. 5. Alternatively a more easily and mechanically adjustable technique may be used wherein a flexible elongated strip 33 is formed into a loop, one part 34 of which is magnetic and the other part 35 of which is non-magnetic. This strip is shown in FIG. 8 which illustrates that there are also sprocket holes 36 formed therein which are engageable by a sprocket 37 that is rotatably mounted to the ring. When the sprocket is turned, variable amounts of magnetic or non-magnetic material may be left in the void.

Experiments have been made to determine the amount of change of effective permeability which can be obtained using the technique of FIG. 5. A permeability change of about was secured when the void in FIG. 1 was filled with a material consisting of six parts of carbonyl iron powder and one part of insulator varnish. By enlarging the groove an even greater permeability change, on the order of about can be obtained. The size of the void is arbitrary, and is selectible for optimum results.

The strip of FIG. 8 may be made of a strip of nylon or mylar for the non-magnetic portion and a strip comprising a mixture of nylon and carbonyl iron having permeability between approximately 5.5 and 4.7 The strip utilized in FIG. 4 may be a strip of nickel iron having a permeability on the order of about 4,000,a. The effective permeability of the ring when made of pressed carbonyl iron will ordinarily be on the order of about 10p, although it may vary from around 7 to about Effective percentage changes, on the order of 040%, may be achieved with the embodiments shown herein.

This invention thereby provides a convenient means for varying the effective permeability of a ring so as to adjust the ring to desired magnetic characteristics.

This invention is not to be limited by the embodiments which are shown in the drawings and described in the description which are given by way of example and not of limitation, but only in accordance with the scope of the appended claims.

I claim:

1. In combination: an annular ring for a toroidal coil, said ring having an axis, a concentric inner and outer wall, and a pair of axially spaced-apart boundary walls, the ring having an internal void extending arcuately within the walls for a substantial portion of the arcuate length of the ring and having access through one of said walls to the void; and a quantity of magnetizable material discretely divided and dispersed in a settable medium set in, but not filling, said void, whereby further adjustment of the permeability of the ring may be made by injection into the void of additional magnetizable material and settable medium.

2. A method of variably adjusting the permeability of an annular ring of magnetic material comprising:

(a) forming a void in the ring extending for a substantial portion of the arcuate length of the ring;

(b) inserting into said void a quantity of magnetizable material in discretely divided form dispersed in a settable medium suificient to change the permeability of the ring from the value it had without the addition of said quantity.

References Cited UNITED STATES PATENTS 2,391,563 12/1945 Goldberg 336-233 XR 2,585,865 2/1952 Somers 336135 XR 2,703,392 3/1955 Rex 336-- 2,716,736 8/1955 Rex 336-221 XR 3,218,591 11/1965 Caruthers 336-136 XR FOREIGN PATENTS 119,191 7/1947 Sweden.

LEWIS H. MYERS, Primary Examiner.

T. J. KOZMA, Assistant Examiner. 

